In a cellular communications network, a user equipment (UE) may communicate with a base station (BS) using a number channels including uplink (towards the BS from the UE) and downlink (towards the UE from the BS) channels. Downlink control channels may transmit, e.g., scheduling information to a UE from the BS.
Conventionally, a user equipment (UE) may attempt to decode candidate control channels in a designated search space. For example, in Long-Term Evolution (LTE), a search space is a set of candidate control channels which a UE is supposed to attempt to decode. There may be more than one search space. In particular, a search space may be a common search space, which is common to all UEs of the cell, or a UE search space, which is typically determined by a non-infective function of UE identity and may thus be shared with some other (though not all) UEs of the cell. In a LTE cell, all search spaces are contained in a constant set of one or more subbands. As a consequence, a LTE base station transmits control channels to all UEs in the same set of subbands. This restricts the scheduler's ability to offload a subband in the set during traffic peaks. It also restricts the scheduler's ability to avoid or reduce interference.